More evidence has weighed in on the fiery debate about the safety of vaping and e-cigarettes, highlighting how many of the fruity flavorings and other additives in e-cigarette liquid appears to increase inflammation and impair lung function. Even more damningly, the new findings showed that short-term exposure to e-cigarette vapor caused levels of short-term lung inflammation similar, if not worse, to that seen in traditional tobacco cigarettes.

The new study, published in the American Journal of Physiology, was carried out on mice (note: not humans) by scientists from the University of Athens in Greece. They divided the mice into four groups and subjected them to whole-body exposure of varying chemical combinations four times each day with 30-minute smoke-free breaks.

One group were exposed to tobacco cigarette smoke, one to flavorless e-cig vapor derived from plant oils called propylene glycol, one to e-cigarette vapor containing propylene glycol and nicotine, and another to e-cigarette vapor containing propylene glycol, nicotine, and tobacco flavoring.

After three days, all of the groups showed signs of inflammation, mucus production, and altered lung function. However, the groups exposed to the vapor containing nicotine and flavorings showed more negative effects with long-term exposure. Furthermore, the group exposed to flavorings showed increased levels of two inflammation-producing proteins, suggesting this component may pose deeper health risks.

“The condition of the e-cigarette groups in comparison with the cigarette group surprised the researchers,” the American Journal of Physiology wrote in a press release. “The level of oxidative stress—stress at a cellular level—in the flavoring group was equal to or higher than that of the cigarette group.”

Before jumping to any bold conclusions, there are a few things to consider when looking at this study. First of all, most obviously, this is a study on mice, not humans. Secondly, it’s hard to compare vaping with being put in a vapor-filled room four times a day with just a 30-minute interval in between. Thirdly, all of the studied effects were short-term effects. Since vaping is such a new trend, there are next to no long-term studies on the phenomenon, which is partly why its safety is so hotly debated.

Nevertheless, this study builds on the mounting evidence that e-cigarettes also carry health concerns of their own, even though the current consensus still argues that they are less unhealthy than smoking cigarettes. In the words of the researchers: "The observed detrimental effects in the lung upon [e-cigarette] vapor exposure in animal models highlight the need for further investigation of safety and toxicity of these rapidly expanding devices worldwide."